For many years, my understanding has been that "ensure" means to guarantee an event or condition, while "insure" means limiting financial liability (typically through insurance). I've noticed this year (as a 1L) that many judges (including even Justice Kennedy in a concurrence in United States v. Lopez) use the word "insure" for both definitions. What do you make of this?

According to Associated Press style, to “ensure” that something happens is to make certain that it does, and to “insure” is to issue an insurance policy. Other authorities, however, consider “ensure” and “insure” interchangeable. To please conservatives, make the distinction. However, it is worth noting that in older usage these spellings were not clearly distinguished.

I would personally distinguish them, but it's not lack of education that results in their conflation.